Process for obtaining fatty acid alkyl esters, rosin acids and sterols from crude tall oil

ABSTRACT

The disclosed invention provides a process for obtaining fatty acid alkyl esters, rosin acids and sterols from crude tall oil (CTO), characterised in that the CTO is subjected to the following steps: (a) reacting the free fatty acids present in the CTO with lower alcohols; (b) separating the fatty acid lower alkyl esters thus obtained from the remaining CTO to produce a first stream of fatty acid esters; (c) esterifying the sterols in the remaining CTO with boric acid; (d) separating the remaining rosin acids from the sterol borates previously obtained to produce a second stream of rosin acids; and (e) converting said sterol borates into the free sterols to produce a third stream of free sterols.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 USC § 365 from International Application PCT/BR2003/000024, filed on Feb. 21, 2003.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention refers to a process for obtaining fatty acid alkyl esters, rosin acids and sterols from crude tall oil (CTO) which involves several esterification and distillation steps.

2. Background Art

The use of sterols to take control of cholesterol level in human nutrition body industry might increase a lot the demand for non-GMO sterols. Consequently, a commercial separation process of sterols from Crude Tall Oil is highly interesting from the economical viewpoint, since this is one of the main source of sterols. Crude tall oil typically comes from the sulphate process employed in the manufacture of cellulose from wood. More particularly, the spent black liquor from the pulping process is concentrated until sodium salts (soaps) of various acids separate out and are skimmed off. The salts are acidified or decomposed with sulphuric acid so as to provide the crude tall oil.

Crude tall oil is refined mainly by vacuum distillation processes to separate the various compounds almost completely into rosin and fatty acid fractions. The current technology is based in distillation where the acids are fractionated in several columns. Using a first column to separate the more volatile fatty acids and rosin acids, from the less volatile materials, which include many of the unsaponifiable and neutral materials such as sterols and their esters. A second column is commonly designed to separate the more volatile fatty acids from the less volatile rosin acids. This process usually ends up with a bottom that is currently called “pitch”, where sterols, heavy hydrocarbons, wax alcohols are the main substances. Commercially, only fatty and rosin acids are produced. Pitch usually is used as a fuel. Due to the high distillation temperature there is significant sterols degradation. Also the most part of the free sterols are converted into esters. Tall oil pitch is a very viscous, dark product, which is rather difficult to handle. So far, there is no economic commercial process running to extract sterols from the pitch. From the state of the art a number of processes are known describing ways to extract sterols from CTO soaps using solvents and distillation processes prior to any acid splitting process, which theoretically could avoid sterols losses. See, for example, U.S. Pat. No. 6,107,456, U.S. Pat. No. 6,414,111, and U.S. Pat. No. 6,344,573. However, these processes are characterised by a high technical effort and were not reduced into practice for economical reasons.

A method of separating sterols from crude tall oil, wherein the sterols are not destroyed in the process, would be a useful invention in the chemical preparation industry. Therefore, the objective of this invention is to find an economic process to separate the three main crude tall oil (CTO) components, fatty acids or their esters, rosin acids, and sterols, to get these commercially valuable products.

BRIEF SUMMARY OF THE INVENTION

The present invention therefore provides a new process for obtaining fatty acid alkyl esters, rosin acids and sterols from crude tall oil (CTO), which is characterised by the following steps:

-   -   (a) reacting the free fatty acids present in the CTO with lower         alcohols;     -   (b) separating the fatty acid lower alkyl esters thus obtained         from the remaining CTO to produce a first stream of fatty acid         esters;     -   (c) esterifying the sterols in the remaining CTO with boric         acid;     -   (d) separating the remaining rosin acids from the sterol borates         previously obtained to produce a second stream of rosin acids;         and     -   (e) converting said sterol borates into the free sterols to         produce a third stream of free sterols.

DETAILED DESCRIPTION OF THE NVENTION

In more detail, in step (a) of the process the fatty acids are converted into their respective C₁-C₄ alkyl esters, preferably into their methyl esters. The major advantage of this step lies in the low boiling point of the esters thus obtained, which makes it easy to separate them from the other fractions. This is preferably done in a single esterification step due to the selective enzymatic or chemical reaction between fatty and rosin acids, with means that usually only the fatty acids are converted into their respective esters. The esterification can be conducted by means of acidic catalysts, like for example methane sulfonic acid at temperatures of 120 to 150° C., or enzymes, like for example Novozym CaLB (Novo) at temperatures of 20 to 50° C., depending on the activity optimum of the micro-organisms. Usually, the enzymatic reaction takes a significantly longer time. The esterification can be carried out under pressure.

In step (b) the fatty acid esters thus obtained are separated from the remaining CTO by means of distillation, short path distillation or fractionation, employing milder conditions compared to the acid distillation. The fatty acid alkyl esters, preferably fatty acid methyl esters, are thereby advantageously obtained without rosin acids contamination and leaving less fatty acids in the bottom stream. The distillation is preferably carried out by means of a wiped film evaporator which is usually conducted at a reduced pressure of 0.01 to 10 mmHg and a temperature of 190 to 240° C.

After the fatty acid methyl esters distillation, boric acid (H₃BO₃) is added to the bottom stream, which contains sterols and rosin acids, to transform all the free sterols into sterol tri-esters (step c). Sterol esters are much more stable than free sterols, which leads to less degradation products, especially those due to the dehydration reaction. By this step it is possible to achieve a better separation between rosins and neutrals and to avoid the unwanted degradation of the sterols. Usually, the esterification is conducted a temperature of 200 to 230° C.

Finally, according to steps (d) and (e), the rosin acids also are separated from the sterol borate esters and other high molecular weight hydrocarbons, preferably by means of a short pass distillation, and more preferably by means of a wiped film evaporator. The latter process is again operated preferably at a reduced pressure of from 0.01 to 10 mmHg and a temperature of 190 to 240° C. After the rosin acids distillation, the borate sterol esters are easily converted to the free sterols through hydrolysis or solvolysis. The preferred solvent, however, is water.

This process can also be applied to the tall oil pitch to enrich the sterols content. The borate esters step can be applied to separate tocopherols and sterols from the fatty acids portion in the soy bean vegetable oil distillate (VOD), and also to separate sterols and high molecular alcohols in the sugar cane waxes. The first stream, fatty acid methyl esters, is used to produce methyl dimerate, a raw material used to make polyamides as described in the U.S. Pat. No. 6,281,373. The second stream, the rosin acids, is used to produce adhesives and other conventional products. The third stream, can be used as high sterols feed in the existent purification sterols processes. The viscosity of this stream can be decreased by adding soy bean oil during the last distillation or by reacting alcohols, C₁₂-C₁₈-saturated or unsaturated during the boric acid esterification step. The alcohols can be recovered after the hydrolysis step.

EXAMPLES Comparative Example C1 Wiped Film Evaporator Distillation of Crude Tall Oil

This example illustrates for comparison purpose a wiped film evaporator (WFE) distillation of crude tall oil (CTO) in the same wiped film evaporator equipment used to develop the entire process, without selective enzymatic or chemical esterification of fatty acid and without transforming all free sterols into sterols borate triesters.

600.0 ml/h of CTO were passed through a WFE. The CTO contained 4.7% b.w. sterol, of which only 9.0% b.w. was already present as sterol esters. The WFE was operated at 1 mm Hg, with a initial residue temperature of 190° C. The residue fraction (residue 1) leaving the bottom of the WFE represented 64.0% b.w. of the CTO feed. The residue 1 contained 38.0% b.w. rosin acids, 40.0 b.w. % of TOFA. In the second distillation, the WFE was operated at 1 mm Hg, with a initial residue 1 temperature of 240° C. The residue fraction (residue 2) leaving the bottom of the WFE represented 15.0% b.w. of the residue 1 feed. The residue 2 contained 40% b.w. rosin acids, and 6% b.w. total sterol. The sterol yield in this process was 25% b.w., which means that 75% b.w. of the sterols were degradated or distilled off together with the rosins and fatty acids.

From this example one can see that is not possible to separate the fatty acids from the rosin acids using short path distillation and also the sterols recovery is too low.

Inventive Example 1 Crude Tall Oil Chemical Esterification and Distillation

This inventive example describes the use of an selective chemical esterification of fatty acid from crude tall oil followed by the wiped film evaporator (WFE) to separate the fatty acids as methyl esters from the remaining heavy products. This is according to the process of the present invention, which avoids the sterols degradation in the residue fraction, and produces a high quality fatty acid ester (TOFA-Me) and rosin acids from the crude tall oil.

(a) Esterification Step

1 kg of CTO obtained from RESITEC Industrias Quimicas LTDA, were placed together with 750 g (23.43 moles) of methanol from Aldrich Chemical Co. and 12 g of methanesulfonic acid (0.12 moles) from Merck KGaA, into a 2-1-Büchi laboratory autoclave BEP 280 equipped with a thermometer, and mechanical agitator. Over a two-hour period, the temperature was maintained at 140° C. The temperature was then reduced from 140° C. to 70° C. and the unreacted methanol distilled off. The maximum reaction pressure in the reaction was 7 bar. The acid value of the CTO was reduced from initially 154 mgKOH/g to 65 mgKOH/g.

(b) Distillation Step

1.0 kg/h of CTO were passed through a WFE. The initial CTO contained 4.7% b.w. sterol, of which only 9.0% b.w. were already present as sterol esters, 40.2% b.w. of rosin acids and 45% b.w. of fatty acids. The WFE was operated at 1 mm Hg, with a initial residue temperature of 190° C. The residue fraction (residue 1) leaving the bottom of the WFE represented 55% b.w. of the CTO feed having 8.6% b.w. total sterols. The sterol yield in this first distillation has been 99.4% b.w. The remaining 0.6% b.w. of the sterols was evaporated along the distillate 1 which had 93% b.w. of TOFA-Me and 7% b.w. of light boilers. Thermal degradation reactions are minimal. Subsequently, 1 kg of residue 1 5.0 g of boric acid (0.08 moles ) obtained from Aldrich Chemical Co., were added. The sample was transferred into a 2-liter, 3-necked round bottom flask for 4 h at 220° C. to convert all the free sterols into esters. After this step the product was distilled through the WFE which was operated at 1 mm Hg, with a residue temperature of 240° C. The residue 2 fraction leaving the bottom of the WFE represented 35% of the CTO feed. The residue 2 had 21% b.w. total sterols. The total sterols yield in the entire process (distillation 1 and 2) was 88% of the theory.

Inventive Example 2 Crude Tall Oil Enzymatic Esterification and Distillation

This example describes the use of a selective enzymatic esterification of fatty acid from crude tall oil and a wiped film evaporator (WFE), as used in accordance with the present invention, to increase the yield of sterols in the residue fraction, and to produce a high quality fatty acid ester (TOFA-Me=tall oil fatty acid methyl esters) and rosinic acid from crude tall oil.

(a) Esterification Step

3 kg of CTO obtained from RESITEC Industrias Quimicas LTDA were placed together with 750 g (23.43 moles) of methanol from Aldrich Chemical Co., 120 g of water, and 1.5 g of Novozym CaLB L from NOVOZYMES Latin America Ltda, in a 4-1-3-necked round bottom flask equipped with a thermometer, a mechanical agitator, and a condenser. The samples were shaken for 180 hrs at 30° C. The initial acid value of 154.0 mgKOH/g was reduced to 64.0 mgKOH/g.

(b) Distillation Step

After the foregoing enzymatic esterification, the product was distilled in the WFE which was operated at 1 mm Hg, with a initial residue temperature of 190° C. The residue 1 leaving the bottom of the WFE represented 54.0% b.w. of the CTO feed. The residue 1 contained 8.8% b.w. total sterols. The sterols yield in this first fractionation represented 99.4% b.w. The remaining 0.6% b.w. of the sterol were evaporated along with the volatile portion of the CTO. Thermal degradation reactions were minimal. Subsequently, to 1 kg of residue 1 5.0 g of boric acid (0.08 moles ) obtained from Aldrich Chemical Co., the sample were added. The sample was transferred into a 2-liter, 3-necked round bottom flask and reacted for 4 h at 220° C. to convert all the free sterols into esters. After the reaction the product was distilled through a WFE operating at 1 mm Hg, with a residue temperature of 240° C. The residue 2 fraction leaving the bottom of the WFE represented 35.0% b.w. of the residue 1 feed having 21% b.w. of sterols. Thermal degradation products were 6.0% b.w. of the total. 

1-10. (canceled)
 11. A process for obtaining fatty acid alkyl esters, rosin acids and sterols from crude tall oil, the process comprising subjecting the crude tall oil to the following steps: (a) reacting the free fatty acids present in the crude tall oil with lower alcohols; (b) separating the resulting fatty acid lower alkyl esters from the remaining crude tall oil to produce a first product stream of fatty acid esters; (c) esterifying the sterols in the remaining crude tall oil with boric acid; (d) separating the remaining rosin acids from the resulting sterol borates to produce a second product stream of rosin acids; and (e) converting the sterol borates into the free sterols to produce a third product stream of free sterols.
 12. The process according to claim 11, wherein the esterification of step (a) is carried out in the presence of an acid catalyst.
 13. The process according to claim 12, wherein the acid catalyst is methane sulfonic acid.
 14. The process according to claim 11, wherein the esterification of step (a) is carried out at a temperature of 120 to 150° C.
 15. The process according to claim 11, wherein the esterification of step (a) is carried out in the presence of one or more enzymes.
 16. The process according to claim 15, wherein the esterification of step (a) is carried out at a temperature of 20 to 50° C.
 17. The process according to claim 11, wherein the fatty acid lower alkyl ester separation step (b) is carried out by distillation.
 18. The process according to claim 17, wherein the distillation of step (b) is carried out by means of a wiped film evaporator.
 19. The process according to claim 11, wherein the rosin acid separation step (d) is carried out by distillation.
 20. The process according to claim 19, wherein the distillation of step (d) is carried out by means of a wiped film evaporator.
 21. The process according to claim 18, wherein the wiped film evaporator is operated at a reduced pressure of 0.01 to 10 mm/Hg and a temperature of 190 to 240° C.
 22. The process according to claim 20, wherein the wiped film evaporator is operated at a reduced pressure of 0.01 to 10 mm/Hg and a temperature of 190 to 240° C.
 23. The process according to claim 11, wherein the esterification of step (c) is carried out at a temperature of 200 to 230° C.
 24. The process according to claim 11, wherein the conversion of the sterol borates of step (e) is carried out by solvolysis.
 25. The process according to claim 24, wherein the solvolysis of the sterol borates of step (e) is affected by means of water. 